Reciprocating piston compressor

ABSTRACT

A compressor including a cylinder, the cylinder delimiting a compressor chamber having a circular cross-section and the cylinder having a longitudinal axis and including a front wall, the front wall of the cylinder having inlet and outlet openings for passage therethrough of a medium to be compressed; and a reciprocating piston disposed in the compressor chamber, the reciprocating piston being reciprocable within the compressor chamber in a movement that includes a dead center position and having a pair of opposed ends with one end being more proximate to the front wall of the cylinder than the other opposed end and the reciprocating piston having an expulsion projection on its one end, the expulsion projection entering the outlet opening in a dead center position of the reciprocating piston, the longitudinal axis of the cylinder extending through the outlet opening.

The present invention relates to a compressor with a cylinder, which contains a compressor chamber having a circular cross-section, in which a reciprocating piston can be moved to and fro. Inlet and outlet openings for a medium to be compressed are both frequently arranged on a front wall of the cylinder. To be able to provide the openings with as large a diameter as possible in relation to the diameter of the front wall, they are mostly arranged on different sides of an imaginary center plane which diametrically crosses the front wall.

To achieve a high degree of efficiency of the compressor, the dead volume thereof has to be as minimal as possible. It is thus known to provide a reciprocating piston compressor with a projection on the surface of the piston which faces the front wall, said projection engaging in the outlet opening on the top dead center of the piston in order to expel medium contained therein from the compressor chamber as thoroughly as possible.

To ensure that the projection of the piston can reliably engage in the outlet opening, the piston in the compressor chamber must not be rotatable about the longitudinal axis thereof. This presents no problem in the case of a conventional reciprocating piston which is driven by a rotating motor by way of a crank gear. With newer compressor models, like the linear compressor known from U.S. Pat. No. 6,505,032 B2 for instance, a rotation of the piston about the longitudinal axis is not ruled out. If such a rotatable piston is provided with a projection in the afore-described manner, there is a danger of the projection no longer entering the outlet opening once the piston has rotated and instead striking the front wall of the cylinder and thereby damaging the compressor.

The object of the invention is to specify a compressor, which achieves a high degree of efficiency without having to exclude from the design a rotation of the piston in the compressor chamber about the longitudinal axis thereof.

The object is achieved in that in the case of a compressor with a cylinder, in which a compressor chamber with a circular cross-section is formed and inlet and outlet openings for a medium to be compressed are formed in a front wall of the cylinder, and with a reciprocating piston which can be moved to and fro in the compressor chamber, said reciprocating piston having an expulsion projection on its surface facing the front wall, said expulsion projection engaging in the outlet opening in a dead center position of the piston, and the longitudinal axis of the cylinder runs through the outlet opening. The central axis is to be understood as a longitudinal axis.

In order to realize a large cross-section in the inlet opening despite the central positioning of the outlet opening, the latter preferably has a non-circular cross-section, the dimensions of which are greater in the peripheral direction of the cylinder than in the radial direction.

The inlet opening can in particular have a cross-section in the form of an arc.

Alternatively, a plurality of inlet openings distributed about the outlet opening may be provided. These are also expediently distributed along an arc.

The arc is expediently concentric in respect of the longitudinal axis. It preferably extends over an angle of less than 180°. The latter is particularly significant in order to be able to shut off the whole inlet cross-section using a single shut-off body.

Such a shut-off body is preferably forced against the inlet opening by means of a first flat spring arranged in the compressor chamber.

To keep the bending load of the flat spring to a minimum, it is expedient to make this as long as possible in relation to the radial dimensions of the compressor. It is particularly expedient here for the flat spring to be fastened to a point on the front wall which is diametrically opposite to the inlet opening.

To prevent the flat spring from shutting off the outlet opening, it is preferably provided with an opening, through which the longitudinal axis of the cylinder runs.

A second shut-off body is preferably forced against the outlet opening by means of a second flat spring arranged on the exterior of the front wall.

The assembly of the compressor is simplified if the first and second flat spring are fastened to the front wall by means of at least one common rivet. Each flat spring is preferably held by at least two rivets in order to reduce the rotation of the flat spring, which could result in the shut-off body no longer correctly covering the assigned opening.

Further features and advantages of the invention result from the description of exemplary embodiments which follows with reference to the appended figures, in which;

FIG. 1 shows a perspective view of a linear compressor according to the invention;

FIG. 2 shows an exploded view of parts of the compressor in FIG. 1; and

FIG. 3 shows a section through the cylinder of the compressor in FIG. 1.

FIG. 1 shows an exemplary design of a linear compressor for a refrigerator, which represents a preferred use of the invention. The linear compressor has a stiff, approximately U-shaped frame seen from the top view, which is composed of two flat wall pieces 1 and an arc 2. A first membrane spring 3 is clamped between front sides of the arc 2 which face one another and two wall pieces 1, a second membrane spring 4 of the same type as membrane spring 3 is fastened to front sides of the wall pieces 1 which face away from the arc 2.

The membrane springs 3, 4 punched from spring steel sheet each have four spring arms 5, which extend in a zigzagged fashion from the wall pieces 1 to a central section 6, with which they coincide. The central section 6 has two bores in each instance, two exterior, upon which a permanently magnetic oscillating body 8 is suspended with the aid of screws or rivets 7 and a central bore, through which a piston rod 10 fastened to the oscillating body 8, e.g. by means of screws, extends in the case of membrane spring 3. The piston rod 10 connects the oscillating body 8 to a reciprocating piston (not visible in the Fig) inside a cylinder 15, which is supported by the arc 2. The refrigerant inlet and outlet ports of the pump chamber are identified with 16 and/or 17.

Two electromagnets 9 with an E-shaped yoke and a coil wound around the central limb of the E are each arranged between the oscillating body 8 and the wall pieces 1 with pole shoes facing the oscillating body 8 and are used to power an oscillating movement of the oscillating body 8. A control circuit 37 provides the electromagnets 9 with an alternating current, the frequency of which is adjusted to the natural frequency of the system which can oscillate, which is formed by the membrane springs 3, 4, the oscillating body 8 and the reciprocating piston powered thereby.

The cylinder 15 is, as apparent in FIG. 1, arranged in a main body 11, in which the reciprocating piston is moved to and fro, a valve plate 12, which forms a front wall of a compressor chamber recessed in the main body and a cap 13, upon which the inlet and outlet ports 16, 17 are positioned.

The design of the cylinder is more obvious with the aid of the exploded representation in FIG. 2. The main body 11 is omitted in FIG. 2; the outline of the compressor chamber which extends through the main body is indicated on the valve plate 12 as a dashed circle 14. The longitudinal axis of the compressor chamber is indicated as a dot-dashed line. A circular outlet bore 18 is arranged in the valve plate 12 exactly coaxially in respect of the longitudinal axis. An arched slot extends through an angle of approximately 120° here about the outlet bore 18 and forms an inlet opening 19 of the compressor chamber.

Further bores 20 at the edges of the valve plate 12 are provided, in order to receive screws (not shown), with which the valve plate 12 and the cap 13 are fastened to the main body 11. Two further bores 21 are used to fasten two flat springs 22 and/or 23 to the valve plate 12 with the aid of rivets 24. The flat springs 22, 23 together with the inlet opening 19 and/or outlet opening 18 each form inlet and outlet valves of the compressor chamber. The flat springs 22, 23 each have an elongated foot 25, in which holes 26 which are complimentary to the bores 21 are formed for the rivets 24 and an elastic guide 27 protruding from the foot in respect of the longitudinal axis.

An opening 28 is cut into the guide 27 of the flat spring 23, which, if the flat spring 23 is riveted to the valve plate 12, releases the outlet bore 18. An end section 38 of the guide 27, which extends in an arched manner about the opening 28, forms a shut-off body of the inlet valve, which covers the inlet opening 19 when the flat spring 23 is relaxed.

The guide 27 of the flat spring 22 rests externally against the outlet bore 18, with its top functioning as a shut-off body of the outlet valve.

The interior of the cap 13 is subdivided into a low-pressure cavity 30 and a high-pressure cavity 31 by means of an intermediate wall 29, into which the refrigerant inlet port 16 and/or outlet port 17 open and which communicate with the compressor chamber by way of the inlet opening 19 and/or outlet bore 18.

The reciprocating piston designated 32 has a projection 33 which is concentric in respect of the longitudinal axis in the perspective view in FIG. 2 of the side facing away from the observer, the length and diameter of which correspond to the common thickness of the valve plate 12 and the flat spring 23 and/or the diameter of the outlet bore 18. At a top dead center of the movement of the reciprocating piston 32, if this touches the flat spring 23 pressed against the valve plate 12 by pressure prevailing in the compressor chamber, the projection 33 engages in the outlet bore 18 and ousts the remaining gas contained therein.

FIG. 3 shows a section through the main body 11 of the compressor chamber and the reciprocating piston 32. It is apparent that the compressor chamber 14 is surrounded by an annular cavity 34, which communicates with the compressor chamber 14 by means of a plurality of small openings 35. The cavity 34 extends in the longitudinal direction of the compressor chamber 14 from the top to the bottom dead point of the reciprocating piston 32. It is connected to the high-pressure cavity 31 of the cap by way of a bore 36 of the valve plate 12 and is supplied with compressed refrigerant in this way, which penetrates in small quantities through the openings 35 into the compressor chamber 14 and thus forms a gas cushion between the walls thereof and the reciprocating piston 32 upon which the reciprocating piston 32 can be moved with minimal friction in a wear-resistant fashion. 

1-12. (canceled)
 13. A compressor comprising: a cylinder, the cylinder delimiting a compressor chamber having a circular cross-section and the cylinder having a longitudinal axis and including a front wall, the front wall of the cylinder having inlet and outlet openings for passage therethrough of a medium to be compressed; and a reciprocating piston disposed in the compressor chamber, the reciprocating piston being reciprocable within the compressor chamber in a movement that includes a dead center position and having a pair of opposed ends with one end being more proximate to the front wall of the cylinder than the other opposed end and the reciprocating piston having an expulsion projection on its one end, the expulsion projection entering the outlet opening in a dead center position of the reciprocating piston, the longitudinal axis of the cylinder extending through the outlet opening.
 14. The compressor according to claim 13 wherein the inlet opening is formed with a noncircular cross-section wherein the dimensions of the non-circular cross-section are greater in the peripheral direction of the cylinder than in the radial direction of the cylinder.
 15. The compressor according to claim 14 wherein the inlet opening is formed with a cross-section in the form of an arc.
 16. The compressor according to claim 13 wherein the compressor is formed with a plurality of inlet openings distributed about the outlet opening.
 17. The compressor according to claim 16 wherein the inlet openings are distributed along an arc.
 18. The compressor according to claim 15 wherein the arc extends over an angle of less than
 180. 19. The compressor according to claim 13 and further comprising a first shut-off body wherein the first shut-off body is forced against the inlet opening by a first flat spring disposed in the compressor chamber.
 20. The compressor according to claim 19 wherein the first flat spring is fastened to a point on the front wall disposed oppositely from the inlet opening.
 21. The compressor according to claim 20 wherein the first flat spring has an opening through which the longitudinal axis of the cylinder extends.
 22. The compressor according to claim 15 and further comprising a second shut-off body wherein the second shut-off body is forced against the outlet opening by a second flat spring disposed on the exterior of the front wall.
 23. The compressor according to claim 19 wherein the first flat spring and the second flat spring are each fastened to the front wall by at least one rivet.
 24. The compressor according to claim 15 and further comprising a linear motor configured for driving piston movement. 